Si la falta absoluta se produce durante los últimos dos años del período constitucional, el Vicepresidente Ejecutivo o Vicepresidenta Ejecutiva asumirá la Presidencia de la República hasta completar el mismo.
You may remember Article 233 from almost exactly six years ago, as Venezuelans wondered whether the winning presidential candidate was either unconscious or dead. This time around the idea is that the legislature has the authority to determine that the president is illegitimate by virtue of, among other things, violating human rights and democratic principles and can call new elections.

This is intended to give the military a legal-constitutional means of forcing Maduro out. If they don't want to, then you can talk about the constitution until you're blue in the face. The opposition is calling for national protests on January 23. Combine that with all the international condemnation, and they hope to push the armed forces.

I won't hazard a guess about what will happen. The safe money is on preservation of the status quo but we just don't know the tipping point of the military. This does seem the most propitious moment for the opposition we've seen in a long time, however.

Update (1/13/19) Now Guaidó has been arrested and his whereabouts unknown. As long as the military is on board, the government can act with impunity.

Update later the same day:government claims it was individuals who did this without authority. Who knows what's exactly going on.